passing form values between forms

Please, do not do what Аslam Iqbal or Manivannan Shan are recommending: it if a bad idea to make any controls on your form public. The reason is simple: when you do that you ties the design of the two forms together - you cannot change form1 without checking that it will not affect form2. You also cannot re-use form2 from form3 because it may not have the same layout or purpose.

Instead, there are two ways to do it:

1) Treat form2 like you would a OpenFileDialog: Show it, wait for the user to press OK and the close form2 and fetch the value in form1. That's easy: Set up a public property which returns the value(s) in the same way the OpenFileDialog supplies FileName

public string Value
   {
   get { return textboxUserInputTo.Text; }
   set { textboxUserInputTo.Text = value; }

Then display your form with

form2 f2 = new form2();
if (f2.ShowDialog() == DialogResult.OK)
   {
   string s = f2.Value;
   ...
   }

2) Set up an event in form2 which says "I have a value for you".

public event EventHandler Changed;

protected virtual void OnChanged(EventArgs e)
   {
   EventHandler eh = Changed;
   if (eh != null)
      {
      eh(this, e);
      }
   }

private void DoSomethingToChangeData()
   {
   OnChanged(null);
   }

Form1 then subscribes to the event.

private void ShowChildForm()
    {
    // Link in his event so if it changes, we detect it.
    form2 f2 = new form2();
    f2.Change += new form2.ChangeHandler(Changed);
    f2.Show();
    }
//
// Fired when the file is changed at a lower level.
//
private void Changed(object sender, EventArgs e)
    {
    form2 f2 = sender as form2;
    string s = f2.Value;
    }